1,829 research outputs found
Algebraic Bethe Ansatz for Integrable Extended Hubbard Models Arising from Supersymmetric Group Solutions
Integrable extended Hubbard models arising from symmetric group solutions are
examined in the framework of the graded Quantum Inverse Scattering Method. The
Bethe ansatz equations for all these models are derived by using the algebraic
Bethe ansatz method.Comment: 15 pages, RevTex, No figures, to be published in J. Phys.
Open t-J chain with boundary impurities
We study integrable boundary conditions for the supersymmetric t-J model of
correlated electrons which arise when combining static scattering potentials
with dynamical impurities carrying an internal degree of freedom. The latter
differ from the bulk sites by allowing for double occupation of the local
orbitals. The spectrum of the resulting Hamiltonians is obtained by means of
the algebraic Bethe Ansatz.Comment: LaTeX2e, 9p
Lattice Kinetics of Diffusion-Limited Coalescence and Annihilation with Sources
We study the 1D kinetics of diffusion-limited coalescence and annihilation
with back reactions and different kinds of particle input. By considering the
changes in occupation and parity of a given interval, we derive sets of
hierarchical equations from which exact expressions for the lattice coverage
and the particle concentration can be obtained. We compare the mean-field
approximation and the continuum approximation to the exact solutions and we
discuss their regime of validity.Comment: 24 pages and 3 eps figures, Revtex, accepted for publication in J.
Phys.
Transfer matrix eigenvalues of the anisotropic multiparametric U model
A multiparametric extension of the anisotropic U model is discussed which
maintains integrability. The R-matrix solving the Yang-Baxter equation is
obtained through a twisting construction applied to the underlying Uq(sl(2|1))
superalgebraic structure which introduces the additional free parameters that
arise in the model. Three forms of Bethe ansatz solution for the transfer
matrix eigenvalues are given which we show to be equivalent.Comment: 26 pages, no figures, LaTe
Thermodynamical limit of general gl(N) spin chains: vacuum state and densities
We study the vacuum state of spin chains where each site carry an arbitrary
representation. We prove that the string hypothesis, usually used to solve the
Bethe ansatz equations, is valid for representations characterized by
rectangular Young tableaux. In these cases, we obtain the density of the center
of the strings for the vacuum. We work out different examples and, in
particular, the spin chains with periodic array of impurities.Comment: Latex file, 27 pages, 5 figures (.eps) A more detailed study of the
representations allowing string hypothesis has added. A simpler formula for
the densities is given. References added and misprint correcte
Reaction Front in an A+B -> C Reaction-Subdiffusion Process
We study the reaction front for the process A+B -> C in which the reagents
move subdiffusively. Our theoretical description is based on a fractional
reaction-subdiffusion equation in which both the motion and the reaction terms
are affected by the subdiffusive character of the process. We design numerical
simulations to check our theoretical results, describing the simulations in
some detail because the rules necessarily differ in important respects from
those used in diffusive processes. Comparisons between theory and simulations
are on the whole favorable, with the most difficult quantities to capture being
those that involve very small numbers of particles. In particular, we analyze
the total number of product particles, the width of the depletion zone, the
production profile of product and its width, as well as the reactant
concentrations at the center of the reaction zone, all as a function of time.
We also analyze the shape of the product profile as a function of time, in
particular its unusual behavior at the center of the reaction zone
Neutrino oscillation experiments and limits on lepton-number and lepton-flavor violating processes
Using a three neutrino framework we investigate bounds for the effective
Majorana neutrino mass matrix. The mass measured in neutrinoless double beta
decay is its (11) element. Lepton-number and -flavor violating processes
sensitive to each element are considered and limits on branching ratios or
cross sections are given. Those processes include conversion, or recently proposed high-energy scattering processes at
HERA. Including all possible mass schemes, the three solar solutions and other
allowed possibilities, there is a total of 80 mass matrices. The obtained
indirect limits are up to 14 orders of magnitude more stringent than direct
ones. It is investigated how neutrinoless double beta decay may judge between
different mass and mixing schemes as well as solar solutions. Prospects for
detecting processes depending on elements of the mass matrix are also
discussed.Comment: 16 pages, 2 figure
Black carp growth hormone gene transgenic allotetraploid hybrids of Carassius auratus red var. (♀)×Cyprinus carpio (♂)
A comparison of genomic profiles of complex diseases under different models
Background: Various approaches are being used to predict individual risk to polygenic diseases from data provided
by genome-wide association studies. As there are substantial differences between the diseases investigated, the data
sets used and the way they are tested, it is difficult to assess which models are more suitable for this task.
Results: We compared different approaches for seven complex diseases provided by the Wellcome Trust Case
Control Consortium (WTCCC) under a within-study validation approach. Risk models were inferred using a variety of
learning machines and assumptions about the underlying genetic model, including a haplotype-based approach with
different haplotype lengths and different thresholds in association levels to choose loci as part of the predictive
model. In accordance with previous work, our results generally showed low accuracy considering disease heritability
and population prevalence. However, the boosting algorithm returned a predictive area under the ROC curve (AUC)
of 0.8805 for Type 1 diabetes (T1D) and 0.8087 for rheumatoid arthritis, both clearly over the AUC obtained by other
approaches and over 0.75, which is the minimum required for a disease to be successfully tested on a sample at risk,
which means that boosting is a promising approach. Its good performance seems to be related to its robustness to
redundant data, as in the case of genome-wide data sets due to linkage disequilibrium.
Conclusions: In view of our results, the boosting approach may be suitable for modeling individual predisposition to
Type 1 diabetes and rheumatoid arthritis based on genome-wide data and should be considered for more in-depth
research.This work was supported by the Spanish Secretary of Research, Development
and Innovation [TIN2010-20900-C04-1]; the Spanish Health Institute Carlos III
[PI13/02714]and [PI13/01527] and the Andalusian Research Program under
project P08-TIC-03717 with the help of the European Regional Development
Fund (ERDF). The authors are very grateful to the reviewers, as they believe that
their comments have helped to substantially improve the quality of the paper
Dynamics of the Universal Area-Preserving Map Associated with Period Doubling: Hyperbolic Sets
It is known that the famous Feigenbaum-Coullet-Tresser period doubling
universality has a counterpart for area-preserving maps of {\fR}^2. A
renormalization approach has been used in \cite{EKW1} and \cite{EKW2} in a
computer-assisted proof of existence of a "universal" area-preserving map
-- a map with orbits of all binary periods 2^k, k \in \fN. In this paper, we
consider maps in some neighbourhood of and study their dynamics.
We first demonstrate that the map admits a "bi-infinite heteroclinic
tangle": a sequence of periodic points , k \in \fZ, |z_k|
\converge{{k \to \infty}} 0, \quad |z_k| \converge{{k \to -\infty}} \infty,
whose stable and unstable manifolds intersect transversally; and, for any N
\in \fN, a compact invariant set on which is homeomorphic to a
topological Markov chain on the space of all two-sided sequences composed of
symbols. A corollary of these results is the existence of {\it unbounded}
and {\it oscillating} orbits.
We also show that the third iterate for all maps close to admits a
horseshoe. We use distortion tools to provide rigorous bounds on the Hausdorff
dimension of the associated locally maximal invariant hyperbolic set: 0.7673
\ge {\rm dim}_H(\cC_F) \ge \varepsilon \approx 0.00044 e^{-1797}.$
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